Project Abstract The opioid epidemic has become one of the most pervasive threats to health and survival in the U.S. Medications for the treatment of opioid use disorders (MOUD) are the gold standard treatment, with robust evidence of effectiveness in reducing opioid use, opioid overdose risk and opioid-related deaths. Nevertheless, retention and adherence to MOUD treatment, particularly buprenorphine (BUP), are discouragingly low; as such, novel, cost- effective, scalable intervention approaches to increase and sustain retention and adherence to BUP treatment are urgently needed. With NIDA support (R34 DA033196), the applicant developed and evaluated, in a RCT, a cognitive behavioral therapy-based short message system (SMS) intervention (TXT-CBT) targeting opioid use and medication adherence among opioid users with HIV. This highly promising intervention demonstrated efficacy in reducing opioid use and increasing biochemically-verified antiretroviral medication adherence, findings that were replicated among HIV-infected alcohol users (R34 AA 022055). The objective of the current research is to adapt and extend this approach to address MOUD treatment retention and adherence. To achieve this, we propose a 2-phase study. In Phase I,: (i) TXT-CBT is adapted, with user and MOUD provider input, to address critical barriers to retention and adherence to BUP treatment, and transported to a scalable, user-friendly SMS platform, to form imFREE (Interactive Messaging for Freedom from Opioid Addiction); and (ii) Usability testing of imFREE is conducted (n=16) in preparation for an effectiveness trial. In Phase II, (i) the effectiveness of imFREE in improving BUP treatment retention and adherence and decreasing opioid use is evaluated in an RCT comparing imFREE to an mHealth education control condition (mHealth ED) among individuals who are initiating BUP, and (ii) we evaluate the cost-effectiveness of imFREE. This application is an excellent fit as a response to RFA-19-006, ?Behavioral Research to Improve MAT: Behavioral and Social Interventions to Improve Adherence to Medication Assisted Treatments for Opioid Use Disorders,? which encourages ?the development of efficacious treatments for substance use disorders that are implementable and self-sustaining, as well as optimal behavioral strategies to promote medication adherence and improve outcomes of pharmacotherapies.? Consistent with the objectives of the RFA, imFREE builds upon the efficacious SMS-based TXT-CBT intervention, with content addressing retention and adherence to BUP, including mitigating risk factors for dropout. imFREE also targets decreased opioid use, with features to notify social and provider support contacts in the face of treatment discontinuation and/or other indicators of relapse and overdose risk. By providing support to maximize BUP treatment adherence, coupled with skills to prevent relapse, imFREE may provide a cost- effective, easily deployable strategy for OUD treatment and prevention of overdose deaths.